In numerous areas of industrial activity, fluid is caused to be exhausted or vented on the occurrence of a selected sequence of events. As an example, in the oil and gas producing industry, many combinations of valves, valve actuators, pilots and other safety devices are utilized to control the flow of through-put, particularly to stop such flow in the event of a dangerous condition. On the occurrence of such an event, such as excessively high or low line pressure, pressurized fluid used to keep the valve open is oftentimes exhausted or vented to remove the necessary pressure, thereby resulting in valve closure. Many times a series of pilots or other controls are used to check on a number of variables. When deviation from the accepted norm occurs, and the valve is closed, it has proved difficult and time consuming to determine, in such situations, which control device, and thereby what problem, triggered closure. This invention was designed to readily provide such information, and utilizes exhaust fluid in a manner heretofore not so used.